The present invention relates to an illuminator for macro inspection, a macro inspecting apparatus, and a macro inspecting method. More particularly to an illuminator, an inspecting apparatus, and an inspecting method which are suitable for not only inspecting dust and scratches on the surface of a wafer, but also visually inspecting the presence or absence of deformed parts caused by local defocusing on the surface of a wafer, which is finely patterned by a photolithographic method.
In a photolithographic process for producing a semiconductor device, various factors such as line width and superposition have to be controlled. In addition, other factors such as resist thickness also have to be controlled so as not to cause defocusing. In order to control these factors, visual inspection for defocusing, size measurement, and overlay measurement are conducted as an in-line inspection of a wafer after resist pattern is formed by each photomask. Generally, in size measurement and overlay measurement, measurement frequency can be reduced as far as photolithographic process is stable. Therefore, only sampling inspection can be conducted in these measurements.
However in a visual inspection for defocusing, all the lots are generally inspected. This is because the visual inspection (macro inspection) can detect deformations of resist patterns due to defocusing, which cannot be microscopically detected in the size measurement or overlay measurement. The term xe2x80x9cdefocusingxe2x80x9d used herein means the phenomenon that deformation of resist patterns is caused by the resist being out of focus in stepper exposure. Such defocusing may be caused by foreign particles adhered onto the surface of a substrate such as a wafer, distortion or deficiencies such as scratches on the surface of the substrate, the difference in resist thickness applied on the surface of a substrate, and the like, which leads to the deformation of resist patterns.
If deformations of resist patterns are early detected, they are peeled off from a substrate, and then the substrate is subjected to a resist-applying step again, thus a commercially available product can be produced without affecting its properties. On the contrary, if visual inspection is not sufficiently effective, detection delay may cause unrenewable yielding loss over several lots.
Thus, visual inspection for defocusing has been quite important in producing semiconductor devices. However, it has also been quite difficult to detect defocusing. In the visual inspection for defocusing, micron-order lines of a resist pattern (finely patterned surface) function as a diffraction grating. When radiation is directed at the lines, normal parts and deformed parts in the resist pattern diffract the radiation differently, so that the color or brightness of diffracted radiation appears differently. However, since there are only slight differences in color and brightness between diffracted radiation, the difference between them is hard to discern. Thus, visual inspection has so far required much time and experience.
In order to solve the above problems, the Japanese unexamined Patent Publication (Patent Kokai) No. 63-305512, No. 62-127652, and No. 10-325805 disclose various automatic inspecting apparatuses. However, conventional halogen lamps are used in these apparatuses, so that light diffracted by a normal position cannot be clearly distinguished from light diffracted by a deformed position. Accordingly, even if light of a predetermined range of wavelength is separated from the diffracted light and then converted into electrical signal by an optoelectronic transducer, detection within a high degree of accuracy cannot be achieved because only a slight difference has to be detected.
The inventors of the present invention compared and evaluated various illuminators for inspection of photoprocessed semiconductor, and found that no illuminator can adequately detect defocusing.
An object of the present invention is to provide an illuminator for macro inspection, which may detect the presence or absence of defocusing problems on a surface of a semiconductor substrate such as wafer, on which resist patterns are finely formed.
Another object of the present invention is to provide an inspecting apparatus and method using the above illuminator.
In the illuminator for macro inspection according to the present invention, radiation is emitted at a predetermined angle from a light source to a surface of a substrate, on which predetermined patterns are formed, so as to determine the presence or absence of deformations on the patterned surface by visually inspecting radiation diffracted by the patterned surface. The emitted radiation may include two different, high color contrast radiation.
It is preferable that these two colors of high color contrast are complementary colors, but it is also acceptable that they are close to complementary colors. The illuminator for emitting radiation can be the one which emits radiation including two different high color contrast radiation from a single light source, or it can also be the one which emits two different high color contrast radiation separately from two different light sources. In addition, the illuminator may comprise two light sources and two kinds of filters for allowing two different high color contrast radiation to separately pass through. Alternatively, the illuminator may comprise one light source and a filter for allowing radiation including two different high color contrast radiation to pass through. Thus, the illuminator can be configured variously.
Two colors of high color contrast, especially complementary colors, produce a sharper contrast than any other combination of two colors, so that glaring and sharp impression is given to human eyes. Examples of complementary color pairs include red and blue green, yellow and blue, green and brown, and the like. Most preferable pair is red and blue green in terms of contrast effect. Two colors of high color contrast include not only complementary colors, but also a combination of two colors close to complementary colors and two colors which produce a sharp contrast in combination. (xe2x80x9ctwo colors of high color contrastxe2x80x9d is hereinafter referred to as xe2x80x9ccomplementary colorsxe2x80x9d unless otherwise specified.)
The radiation applied to the substrate by the illuminator can be obtained as synthesized radiation including two different complementary-color radiation emitted from a single light source. As such an illuminator, it is preferable to use a halogen lamp having a color temperature of 1500K to 3500K and including red light with a wavelength of 677 nm and blue green light with a wavelength of 495 nm. Particularly, a halogen lamp having a color temperature of 2200K is preferable. In addition, an illuminator preferably comprises a yellow filter, as yellow is a color obtained by combining red and blue green.
Alternatively, the radiation applied to the substrate by the illuminator can be obtained as a single light by combining two different complementary-color radiation emitted separately from two different light sources. As such an illuminator, it is preferable to use an illuminator having a system in which red light and blue-green light are emitted and combined, or a system in which two radiation obtained by allowing radiation to pass through a red filter and a blue-green filter are combined.
Alternatively, the radiation applied to the substrate by the illuminator can be obtained as flashing light by repeatedly and alternately flashing two different complementary-color radiation emitted from a single light source. As such an illuminator, it is preferable to use an illuminator comprising two kinds of filters for allowing two different color radiation to pass through, and these filters are preferably movable filters which are arranged in such a manner that an optical path is alternately intercepted by them. Thus, various kinds of illuminators can be used to inspect the surface of the substrate not only for defocusing but also dust and scratches. Particularly, illuminators can be useful to inspect the surface of the substrate for fine scratches produced in a step of flattening a surface of wafer and in a step of peeling resist.
The macro inspecting apparatus according to the present invention comprises: an illuminator for macro inspection which emits radiation; supporting means for supporting a substrate having a surface on which predetermined patterns are finely formed and to which the radiation is applied by the illuminator at a predetermined angle; and determining means for determining whether the predetermined patterns on the surface of the substrate are deformed or not by visually inspecting radiation diffracted by the finely patterned surface. The illuminator for macro inspection emits light including two different complementary-color radiation.
The surface of the substrate on which predetermined patterns are finely formed may function as a diffraction grating for diffracting and reflecting radiation when they are applied to the patterned surface. Where the patterns are uniformly formed on the substrate and there is no deformation in patterns, all the radiation applied to the patterned surface are diffracted and reflected in the same direction. Although it depends on visual angle, either one of two different complementary colors or a color obtained by synthesizing two different complementary colors appears on the whole of the patterned surface. Specifically, when the substrate (finely patterned surface) is rotated relative to the radiation, one of two different complementary colors, a color obtained by synthesizing two different complementary colors, the other of two different complementary colors, and a color obtained by synthesizing two different complementary colors appear in this order.
On the contrary, where there is some deformed patterns on the substrate due to defocusing, either one of two complementary colors appears on the whole of patterned surface while the other of two complementary colors appears locally on the surface. Unlike the above case, when the substrate (finely patterned surface) is rotated relative to the radiation, one of two complementary colors appears locally in the other color. For example, where the two complementary colors are red and blue green, the parts where red appears locally in blue green or blue green appears locally in red are deformed parts, so that deformed parts can be easily detected. Thus, a sharp contrast produced by complementary colors makes it much easier to visually inspect the surface of the substrate for deformed parts due to defocusing.
In the illuminator for macro inspection according to the present invention, two different high-contrast color radiation, especially radiation of two colors complementary to each other, are used. Since the finely-patterned surface of the substrate, to which radiation is applied, functions as a diffraction grating, the color of light diffracted by normal parts is the one color of a complementary color pair, and the color of light diffracted by deformed parts in the other color of the pair. Such complementary colors are vivid and have a sharp contrast, so that visual inspection can be easily conducted. Thus, the present invention makes it possible to visually inspect the surface of the substrate for deformed parts, even if there are only a few deformed parts. Experiments proved that the illuminator of the present invention made it possible to visually observe 5% (about 0.05 xcexcm) of changes in a resist pattern.
Thus, the present invention makes it possible to visually inspect a surface of a substrate for deformed parts on a process line even if there are only a few deformed parts. Therefore, a failure of production equipment can also be detected at an early stage, so that defective items can be minimized and yielding loss can be reduced by recycling the defective items.